Soldering filler metal

ABSTRACT

Tin-lead alloys used for soldering and plating metal wires are improved in their resistance to oxidation when they contain a small amount of aluminum.

United States Patent Hamaguchi et al.

[ Feb. 22, 1972 [54] SOLDERING FILLER METAL [72] Inventors: lhchlro Hamaguchl; Mluo Sch-shill;

Mamoru Koyama, all of Osaka, Japan [73] Assignee: Talsuta Electric Wire & Cable Co., Ltd.,

Osaka City, Japan 22] Filed: 111111.23, 1970 21 Appl.No.: 22,016

[52] US. Cl. ..75/134 B, 75/166 D, 75/175 R [51] Int. Cl. ..C22c 11/00, C22c 13/00 [58] FieltlofSearch ..75/l66 D, 175 R, 1348 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-E. L. Weise Attorney-Wenderoth, Lind & Ponack [57] ABSTRACT Tin-lead alloys used for soldering and plating metal wires are improved in their resistance to oxidation when they contain a small amount of aluminum.

Q No Drawings soumnmo FILLER METAL The present invention relates to an improvement in soldering filler metals and, more particularly, to a tin-lead solder alloy wherein a small amount of aluminum is added so as to impart the resistance against oxidation thereto. inasmuch as the improved tin-lead solder alloy of the present invention concerns, the present invention also relates to a metal wire plated therewith in a plating bath whereby resistance against oxidation is imparted to said metal wire.

it has been known in the art that solders used in metal plating and soldering processes are susceptible to oxidation in their molten state in the air. if no attention is paid to this fact during the soldering or plating operation, an oxide layer is formed on the deposited solder or on the solder plated surface of a metal wire or the like.

in the case where a metal wire or the like article is to be plated with solder alloy by immersing it in a plating bath containing therein molten solder alloy, an oxide film should not be formed on the surface of molten solder alloy in the plating bath, or otherwise the final plating on the wire or the like article is disadvantageously affected. Thus, when the oxide film is formed on the molten surface it has been a common practice to remove the oxide film by sweeping off or by overflowing the molten solder alloy in the plating bath so as to maintain the molten surface in the fresh state throughout the plating operation.

This is particularly true of the case where an electric circuitwiring printed base for use in electric instruments or appliances is soldered or solder plated.

The solder plated wire is largely employed as a lead wire in electronic instruments because of its favorable solderability. Most such plated lead wires to be connected with electric parts such as resistors and condensers are coated with synthetic resin. in this instance, since the coating process is performed under an elevated temperature for a relatively long time, there has been a tendency that the deposited solder alloy is remolten and the deposited solder alloy is oxidized resulting in reduction of the solderability.

in order to overcome the above-mentioned problem, wire plated with high-temperature solder alloy has been employed. lloweve r, no provision for preve n ting the solder plated wire from being oxidized has been made even for high-temperature solder plated wire.

Therefore, it is an object of the present invention to provide an improved oxidation-resistant solder alloy comprising aluminum in the amount of about 0.005 to 0.2 weight percent, tin in the amount of about 0.2 to 99 weight percent, and lead in the amount of the remaining weight percent, wherein resistance against oxidation is imparted to an extent that, even if it is in its molten condition, or at a high temperature slightly lower than the melting point thereof, an oxide film is hardly formed on the surface of the deposited solder.

It is another object of the present invention to provide a metal wire plated with an improved solder alloy, said improved solder alloy comprising aluminum in the amount of about 0.005 to 0.2,weight percent, tin in the amount of about 0.2 to 99 weight percent, and lead in the amount of the ever, for this purpose,

remaining weight percent, wherein the resistance against the oxidation is imparted to an extent that, even if the solder plated wire is exposed in the air at the high temperature for a relatively long time, good solderability is maintained. Howit is preferred that the percentage of aluminum not exceed about 0.1 percent, the other limits being as stated above.

The solder alloys of the present invention can be obtained by adding a small amount of aluminum in the tin-lead mixture during the manufacturing process.

The present invention will be hereinafter fully described by way of example.

EXAMPLE 1 numbered, for the purpose of comparison in respect of the formation of an oxide film on the surface of the molten solder al- 5 loys under the conditions as referred tom Table I.

TABLE I Heating conditions Composition of solder Amount Liquldus Liquldus alloys of aluline plus line plus (weight minum 50 C. 75 0. percent) added (weight Time A Time B" Time A Time 13" Sn percent) (second) (second) (second) (second) 5 40 4 32 5 0. 005 6 43 5 35 5 0. 01 125 368 122 250 5 0.1 7,200 7,200 7,200 7,200 5 0.15 7,200 7,200 7,200 7.200 0 7 50 5 42 15 0. 005 19 228 14 157 15 0.01 813 1, 297 621 1, 003 15 0.1 7,200 7,200 1,200 7,200 15 0.15 7,200 7,200 7,Z00 7,200 0 9 48 5 38 30 0. 005 30 110 21 88 30 0. 01 748 I, 125 605 989 30 0.1 7,200 7,200 7,200 7,200 30 0.15 7,200 7,N0 7,200 7,200 40 0 8 48 6 40 0. 005 25 172 15 130 40 0. 01 645 908 498 851 40 0.1 7,200 7,200 7,200 7,200 40 0.15 7, 7,200 7,200 7.200 50 0 325 747 33 04 50 0.1 7,200 7.200 7,20 7, 50 0.15 7,fl)0 7,200 7,200 7,200 62 0 501 1, I32 181 312 62 0.1 7.20 7,200 7,200 7,2m 62 0.15 7,'J00 7,'b00 7,Z00 735!) B5 0 25 48 7 2] Mil 0.1 77,200 17,2510 /7,l. l0 no 0.11, ,mm 13; 17.7.00 ,mm

It should be noted that the amount of aluminum added is based on the weight percentage relative to the total weight of each tinllead solder alloy. And, in Table I, indicates the time necessary for the oxide film to appear on at least a portion of tin and the other consisting of 60 percent lead and 40 percent tin, were plated on the same wires in the same manner.

The copper wires applied with the improved solder alloys and the conventional solder alloys were heated to the the surface of each molten solder alloy while indicates the 5 specified temperatures in the air. The results of this test in time necessary for the oxide film to appear on the entire surrespect to resistance against oxidation and solderability are face thereof. tabulated in Table ll.

According to Table I, it will be clearly understood that the in sp t t ka il y. there w r f und n differences features of the present invention can be attained when the ween applications of the solder alloys with aluminum amount of aluminum added equals and exceeds 0.005 weight added and the solder alloys without aluminum while the finish percent. However. though the maximum amount thereof is of wires plated with each of the solder alloys with aluminum preferably restricted to not more than 0.2 weight percent, added was superior to that of each of the solder alloys without even if it exceeds 0.2 weight percent, oxidation prevention cfaluminum. fects can be obtained. The reason for the 0.2 limit i that ex- Alternatively, a plating of conventional solder alloy may be cess over 0.2 weight percent may cause problems in respect of formed on the peripheral surface of a copper wire before a workability and others. secondary plating of the improved solder alloy is formed Therefore, according to the present invention, the improved h r solder alloy has not only good re i tan e agai t id tion In general, an increase in the lead content tends to permita when molten, but also is hardly susceptible to oxidation even if decrease n the aluminum n n ut an Increa e in the tin exposed to the air for a much longer time undera temperature content makes It Preferable l0 lnCfeflSe h mount of aluslightly lower than the melting point thereof. This fact implies -U.- that, even when the solidified solder alloy of the present inven- As herein fully disclosed, in the case where solder plating is tion is subsequently subjected to a heat treatment ro e no intended with the use of the solder alloys of the present invenoxide film is formed on the surface thereof with reduction of tion, the cleaning of the surface of molten solder alloys in a its solderability. plating bath is eliminated or lessened. In addition, excellent resistance against oxidation is imparted to the solder plated EXAMPLE ll materiaL With the use of the improved solder alloys numbered 5 and g Presen; mvemlon can be advantageously apphed 15 in Table l, namely, one improved solder alloy consisting of m oflceme 85 percent lead and 15 percent tin having added thereto alue 6 1. An alloy consisting essentially of aluminum in the amount mtnum In the amount of 0.005 welght percent relative to the of about 0.005 to 0.2 weight percent, tin m the amount of total weight of lead and tln and the other consisting of 60 perabout 0 2 to 99 Wei ht ercent and the remainin metal bein cent lead and 40 percent tin having added thereto aluminum g p g g lead. in the amount of 0.1 weight percent relative to the total weight 2 The ano of claim l Wh in the ma imum amou t f of lead and tin, copper wires of 0.7 mm. in diameter were lm'ninumis Wei ht f X n 0 plated in accordance with the ordinary plating method. a g p For the purpose of comparison, two conventional tin-lead solder alloys, one consisting of 85 percent lead and l5 percent TABLE II Composition of solder Amount alloys of alu- (welght minum percent) addgt Testing conditions and results Welg Pb Sn percent) 170 O. 4 hours 200 0., 2 hours 230 0., 1 hour 260 0., 0.5 hour 85 16 0 Appearance: No color change. Ap earance: slight black. Appearance: black. Solder- A z 1 k.

60 40 0 Soderabillty: excellent. figderabllity: good. ability: unfavorable. iiiiiiiri ifnr i mbig o o 86 15 0.006 .do Appearance: no color change. Appearance: no color A a -a ;d k

Solderability: excellent. change. Solderability: g ility ei cell itt. Solder excellent. 40 0. 1 .do .410

NoTE.-The amount of aluminum added is the weight percent relative to the total weight of lead and tin. 

2. The alloy of claim 1 wherein the maximum amount of aluminum is 0.1 weight percent. 